The invention relates generally to rolls for treating webs of material and, more particularly, to an improved seal arrangement for sealing the transverse end of a hydraulically supported roll.
Hydraulically supported rolls typically have a rotatable hollow cylinder forming the working roll circumference and a stationary crosshead extending lengthwise through the hollow cylinder to form an annular clearance space with the inner circumference of the hollow cylinder. Hydraulic support means are provided in the annular clearance space for supporting the hollow cylinder. Transverse end seals are mounted at the ends of the hollow cylinder to seal the annular clearance space from external pressure.
The internal hydraulic pressure can be produced by a hydraulic supporting system that includes a chamber shaped as a semi-cylindrical shell that is pressurizable with hydraulic fluid. This chamber is isolated from the rest of the clearance space by the transverse end seals and by longitudinal seals that extend at diametrically opposite sides of the crosshead between the transverse end seals. Such an arrangement is disclosed in Japanese Utility Model 62-17520. A transverse end seal similar to the above-mentioned seal is also disclosed in DE-PS 20 25 777.
In the above-mentioned documents, the transverse end seal defines the so-called "S-roll chamber", which is in the form of a semi-cylindrical shell divided by longitudinal seals and extends in the circumferential direction over approximately 180.degree.. The use of a transverse end seal extending over approximately 180.degree. is also disclosed in DE-PS 30 03 395, in which the pressure in the S-roll is modified by sealing elements that maintain regions of lower pressure.
In other rolls, such as are disclosed in DE-OS 36 40 902, the clearance space between the hollow roll and the crosshead is filled with hydraulic fluid over a 360.degree. region. In these cases, of course, the transverse end seal also extends over 360.degree..
In many cases, the pressure exerted against the transverse end seal is as great as several tens of bars. The transverse end seals typically include a slide ring mounted on the stationary crosshead and an abutting counter-ring that rotates with the hollow cylinder. The circumferential speed of adjacent, relatively rotatable faces of the rings may be up to 1000 m/min, and the hydraulic fluid may reach a temperature of 250.degree. C. or more. It has been found that under these harsh conditions the hydraulic fluid on the high pressure side of the slide ring tends to flow in a radial direction to the region underneath the slide ring. The pressure of the hydraulic fluid then lifts the slide ring off the fixed counter-ring, thus breaking the seal.